This invention relates to a process of forming a cap flange structure, and is particularly directed to a process of forming stiffened panel structures, especially sinewave I-beam structures.
The use of complex structures such as cap flange and I-beam structures have been prevalent in the aircraft industry for many years, e.g. in the construction of wings, wall panels, and the like. A particularly useful form of stiffened structure of this nature are sinewave I-beam structures, that is I-beam structures wherein the web between the opposite flanges has a sinewave configuration.
Certain metals and alloys exhibit superplasticity and are capable of being subjected to superplastic forming to produce parts of predetermined shapes. Superplasticity is the capability of a material to develop unusually high tensile elongation with reduced tendency toward local necking during deformation. Prior to such superplastic forming, diffusion bonding of the metal workpieces is carried out to bond the workpieces in certain preselected areas, to permit superplastic forming to be carried out in the unbonded areas of the workpieces.
Examples of metals which can be diffusion bonded and which have superplasticity characteristics include titanium, zirconium, refractory metals, and alloys thereof. Aluminum may also be suitable for this purpose, since recent developments indicate that aluminum and its alloys can be diffusion bonded, as well as being capable of superplastic forming.
Using superplastic forming techniques, and employing a die having a sinewave configuration, a panel or beam having a sinewave shape can be formed. Such structure is to be used as the web for an I-beam, for example, wherein a Tee cap or cap flange is required to be mechanically connected along opposite edges of the web. This type of I-beam structure has the disadvantages of increased weight, and presenting problems in connecting the cap flanges to the web, and the resulting connections between the cap flange and web are often not sufficiently secure and positive connections.
U.S. Pat. No. 4,509,671 to Weisert discloses a method of producing structures having preselected shapes such as T-caps by diffusion bonding and superplastic forming.
U.S. Pat. No. 4,361,262 to L. Israeli, discloses a process that may be used as a substitute for superplastic forming. The process is called "accordion expansion" and essentially involves the unfolding of core sheets with a minimal amount of expanding. The formed sandwich structures generally have a vertical core that is linear and flat, although angled core is also possible. To form such structures only about 10% expansion is required. Since almost all metals will expand 10% without a significant loss of strength at elevated temperatures, accordion expansion is not limited to superplastic materials. A major advantage of accordion expansion is that forming can occur at temperatures and pressure differentials significantly lower than superplastic forming.
U.S. Pat. No. 4,582,244 to Rainville discloses a method for forming sine wave I-beams employing diffusion bonding and superplastic forming.
U.S. Pat. No. 4,588,651 to Israeli discloses a method of forming complex structures such as sandwich structures employing an accordion expansion process.
It is an object of the present invention to provide a novel process for producing a cap flange structure.
Another object of the invention is the provision of a process for producing a cap flange structure wherein the cap flange is integrally mounted on a supporting web.
Yet another object is to provide a process for producing an I-beam structure wherein opposite flanges are integrally mounted on the web of the I-beam.
A still further object is to provide procedure for producing an I-beam structure having a web of sinewave configuration, and wherein the flanges along opposite edges of the web are integrally attached thereto by accordion expansion.
Still another object is the provision of procedure for producing the above-noted sinewave I-beam structure wherein the flanges are mounted at an angle of 90.degree. or other than 90.degree. to the central plane of the web.
Other objects and advantages of the invention will appear hereinafter.